The rapid increase in use of e-cigarettes among youth has emerged as an alarming public health concern. Significant health implications of e-cigarette use in adolescent populations include acute and chronic effects on brain development, exposure to harmful genotoxins and carcinogens, and life-long nicotine dependence that can lead to hypertension, cancer, stroke, cardiovascular disease, and reproductive disorders. Concern has also been raised about the potential for e-cigarettes to serve as a gateway to experimentation with traditional tobacco products by youth. Manufacturers of e-cigarettes have targeted vulnerable youth populations, including ethnic minority youth, with extensive marketing campaigns on television, through the internet, and in print media. Given the relatively short period of time e-cigarettes have been available in the United States, little is known about young people's understanding and use of this product, especially among minority youth populations. It is critical to develop a clearer understanding of what minority youth know and believe about e- cigarettes, including perceived social norms about their use and acceptability, misconceptions about their safety, and exposure to targeted marketing efforts. We propose to conduct a mixed-methods study to assess ethnic minority high school students' use and understanding related to e-cigarettes. Guided by our adaptation of the Youth Resilience Framework, we will utilize a combination of qualitative and quantitative methodologies to investigate e-cigarette use and understanding among a large majority-minority high school population in Los Angeles that includes Latino, African American, Filipino, and other Asian students. Specifically, we aim to: 1) Assess current and ever use, and intention to use e-cigarettes among ethnic minority high school students; 2) Assess knowledge, attitudes, and beliefs regarding the health implications of e-cigarettes and perceived social norms about acceptability of their use; 3) Compare predictors of use, knowledge, attitudes, beliefs, and perceived social norms across ethnic groups; and 4) Identify sources of exposure and reactions to e-cigarette marketing, including any ethnic differences. In order to achieve these aims, we will conduct focus groups with ethnic minority high school students, develop a web-based survey by adapting and modifying reliable and valid items from existing youth tobacco questionnaires and results from our focus groups, and administer the web-based survey to 600 ethnic minority high school students. We will then analyze our qualitative and quantitative data to characterize the sample with regards to knowledge of e-cigarettes, relevant attitudes, beliefs and perceived social norms regarding e-cigarettes, the frequency of e-cigarette experimentation and use, and to identify factors associated with using e-cigarettes. The findings from our proposed project will serve as the foundation for developing and testing prevention interventions for ethnically diverse populations of young people.